The present invention relates generally to delivery of digital information to subscriber premises and more particularly to providing this access without substantial new wiring expense.
The delivery of digital video services to the home represents one important aspect of the much publicized xe2x80x9cinformation highway.xe2x80x9d These services include HDTV, video-on-demand (VOD), near-video-on-demand (NVOD) providing staggered program starting times, interactive video services (IVS), and other digital variants of conventional broadcast services.
One of the main obstacles to the introduction of these services is development of the necessary infrastructure for delivering digital video information to the subscribers"" premises. Video services, even with the use of modern compression standards such as MPEG-1 and MPEG-2, intrinsically require large bandwidths. Somehow an infrastructure must be constructed to distribute the necessary signals to individual subscriber premises. At a minimum, each subscriber should be able to select from among numerous digital video programs as can be done now with analog broadcast television.
Various solutions have been proposed. In one scheme, the digital data are distributed via an asynchronous transfer mode (ATM) network to each subscriber""s premises. The physical medium of the ATM network may be implemented in more than one way. One way is to lay optical fiber to each home. Alternatively, fiber may be laid up to the curb, from which point a coaxial cable can relay the ATM cells. The advantages of this technique are the low latency and flexibility of the ATM technology and a large bidirectional bandwidth sufficient to distribute numerous interactive digital video programs. Nonetheless, this approach is practically infeasible today since the cost of laying fiber or coaxial cable to each home is prohibitive. Additionally, the time required to deploy such an infrastructure over a large geographic area makes the scheme even more unattractive.
An alternative scheme is the so-called hybrid fiber coax (HFC) scheme. The HFC scheme provides a two-level network. At the higher level, optical fibers are used to distribute digital information to a plurality of Cable Headends or Host Digital Terminals (HDT). Each Headend or HDT in turn distributes information to multiple hybrid fiber coaxial cables, each of which serves several hundred subscriber units in a bus/loop architecture. The return channel over the coaxial cable is also shared by multiple subscriber units by employing Time Division Multiplexing (TDM). Again, for those network providers that do not already have such an infrastructure installed, costs are prohibitive because coaxial cable must be brought to each home. Furthermore, the use of TDM coupled with highly limited bandwidth gives rise to a large latency in the return channel. Network security is another drawback of the HFC architecture as several users share a single coaxial cable, a particular concern for interactive services that may require transmission of a subscriber""s private information.
Other schemes take advantage of the existing telephone network by using ADSL technology to transfer high data rate information, such as video, over existing telephone company twisted pair lines to subscriber premises. Optical fiber may be used to transfer digital information to the telephone company central office or to a curbside interface where the twisted pair lines begin. The latter architecture is commonly referred to as Fiber-To-The-Curb (FTTC). Alternatively, fiber may be deployed till the basement of a large building, from which point existing twisted pair lines can establish connection with each subscriber. Such an architecture is commonly referred to as Fiber-To-The-Building (FTTB). The disadvantage of this approach is that ADSL provides insufficient bandwidth. Most current ADSL trials carry only 1.5 or 2 Mb/s over twisted pair. Laboratory demonstrations have shown that in the next few years cost effective solutions that provide up to 25 Mb/s may be possible, but even this would be insufficient to provide a broadcast or NVOD service with an acceptable number of service selections. Approaches which bring fiber to the curb carry the added cost of laying the fiber.
Prior art digital data delivery schemes that use relatively narrow bandwidth connections to the subscriber premises require point-to-point sessions between the ultimate server and subscriber unit. This is because the narrow bandwidth link that is closest to the subscriber permits only a point-to-point connection if the desired service quality is expected to be reasonable. These point-to-point sessions waste bandwidth since the server must separately transmit to multiple subscriber units requesting the same program. If the user wishes to switch channels, there is significant extra latency resulting from the need to end the previous point-to-point session before beginning a new one. Furthermore, the network and server hardware needed to accommodate point-to-point sessions is particularly complex and expensive.
The invention provides a network architecture for distributing digital data to subscriber units wherein selection from among multiple digital services is accomplished by transmitting a tuning command from a subscriber unit to one or more intermediate interfaces in a series of links interconnecting the subscriber unit and a server. An example of such digital data is digital video and the services could be multiple digital video programs. The network architecture of the present invention is capable of providing public broadband access without the use of very high bandwidth access lines to subscriber premises.
Using the information received from the subscriber unit, the intermediate interface selects the desired digital service from a multitude of services available in a broadband link coupled to the interface""s input and transmits it to the subscriber unit over a bandwidth-constrained link. The bandwidth-constrained link may be implemented with existing infrastructure, yet the subscriber unit may readily access a wide variety of digital services available on the broadband network. The present invention thus combines universal broadband access with low cost.
In accordance with the invention, a service provider may offer broadcast services over the network in addition to point-to-point interactive services. The broadcast services may be offered without requiring multiple point-to-point sessions from the server to each requesting subscriber unit. Instead, a single copy of a digital stream provided via the broadband link is sufficient to service multiple subscriber units which request it via their intermediate interfaces, thus conserving bandwidth. By contrast, in the prior art point-to-point schemes, the broadband network would be forced to carry a separate point-to-point connection for each requesting subscriber unit.
Note that the present invention provides the advantages of forgoing point-to-point connections for broadcast purposes without requiring the construction of the very high bandwidth links necessary to continuously transmit each available program to each subscriber unit. Thus digital broadcast and NVOD services may be provided effectively and at low cost.
In accordance with one aspect of the present invention, a conventional telephone network is enhanced to provide universal high bandwidth digital service. Typically, telephone service is provided to subscriber premises via individual access lines extending from the subscriber premises to a neighborhood hub or pedestal. The access lines are private and secure twisted pair lines. The pedestal is fed by a high data-rate trunk line, typically implemented as a fiber optic connection.
High bandwidth digital service, including video programming, is transmitted over a twisted pair connection by implementing Asymmetric Digital Subscriber Link (ADSL) modulation and demodulation over the connection which allows for transmission of high speed digital data in a manner that is transparent to existing telephonic traffic, as is well known to those of skill in the art. The network equipment for ADSL modulation and demodulation typically resides in the pedestal.
In accordance with this aspect of the present invention, the pedestal is further specially adapted to receive tuning information from a subscriber unit to which it is coupled by an access line. The pedestal uses the tuning information to select the specified digital data from the multitude of service data received over the broadband network at its inputs to be relayed to the subscriber unit.
In accordance with the present invention, this architecture could be further extended by including one or more additional interfaces. For example, in addition to the pedestal, an interface could be provided within the telephone company central office. The overall video distribution scheme would then incorporate three interconnected layers. The lowest layer would constitute the individual narrow bandwidth access lines between the pedestals and subscriber premises, the middle layer would constitute an intermediate bandwidth link between the central office and the pedestal, and the top layer would be a broadband network feeding the central office or some other broadband source, e.g., a satellite feed. With this scheme, the tuning function could be shared between the pedestal and the interface within the central office. The pedestal would respond to a tuning command from a subscriber unit by attempting to extract the desired program from the intermediate bandwidth network. If the desired program is not already available via the intermediate bandwidth link, the pedestal signals the central office interface to retrieve the program from the broadband network. Of course, this multilayer architecture could be extended indefinitely over any number of interfaces and layers.
The capacity of the intermediate bandwidth link would limit the number of different choices that could be selected simultaneously by subscribers serviced by the same pedestal. For example, the intermediate bandwidth link could carry a fixed number of NVOD channels with each subscriber able to choose one for current viewing. However, not all of the NVOD channels available via the intermediate bandwidth link are likely to be viewed simultaneously. In accordance with the invention, additional digital services may opportunistically exploit intermediate link capacity left unused by current subscriber activity. These additional services could include other broadcast and NVOD channels, VOD service, or interactive services.
In accordance with the present invention, this opportunistic bandwidth scheme could also be adapted to operate in the context of a loop or bus architected access line network, such as a hybrid fiber/coaxial (HFC) network, providing digital broadcast, NVOD or other interactive services. In a HFC network a Host Digital Terminal (HDT) or Cable Headend couples a broadband optical network to one or more HFC cables each of which serves multiple subscriber units in a loop/bus architecture. The HDT or Cable Headend can be modified in accordance with the invention to incorporate an interface that passes only that digital service that has been requested by a subscriber unit as opposed to the prior art method of carrying all the streams belonging to a broadcast or NVOD offering. If bandwidth remains on the cable, additional services can opportunistically exploit it.
Numerous other combinations of layers and interfaces are possible within the scope of the present invention. For example, the broadband network may be implemented as one or more satellite or MMDS (Multichannel Microwave Distribution System) feeds. A video distribution system in accordance with the present invention may also be easily extended to provide interactive services. Alternatively, information besides video information could be distributed. For example, interactive internet services may be provided over the same network that incorporates the present invention.
In accordance with another aspect of the invention, statistical multiplexing is extended to optimize usage of the output bandwidth of broadcast equipment, such as NVOD servers and MPEG multiplexers. This aspect of the invention is independent of network architecture.